SystemEvent:
| {
id: number;
kind: "joined";
seq: number;
timestamp: number;
user: object;
}
| {
id: number;
kind: "left";
seq: number;
timestamp: number;
user: object;
}
| {
id: number;
kind: "present";
seq: number;
timestamp: number;
users: object[];
}
| {
id: number;
kind: "info";
seq: number;
text: string;
timestamp: number;
}
| {
id: number;
kind: "error";
seq: number;
text: string;
timestamp: number;
}